Methods for Flow Reserve:Selective coronary angiography is performed using standard technique with 5F diagnostic catheters in the LCA and RCA. The artery or interest determined by the abnormal area of myocardial perfusion by SPECT or MR imaging will be interrogated. The artery of interest will be cannulated with a 6F or 7F Guide catheter. A 0.014 in x 300cm pressure and Doppler-tipped guidewire (CombMap XT, Volcano Corp) will be advanced into the distal bed of the vessel of interest. After optimization of the pressure and Doppler signal, velocity and pressure measurements will be obtained at rest and after induction of maximal hyperemia with an intravenous bolus of regadenoson. Coronary flow reserve (CFR) will be measured in the target vessel of interest after 1-2 minutes following the IV bolus. Absolute CFVR will be calculated as the ratio of hyperemic to baseline average peak flow velocity and the relative CFVR as the ratio of the absolute CFVR in the target vessel to the absolute CFVR in the reference artery. FFR and CFR values will be categorized according to published cut-off values of 0.75 and 2.0, respectively.